Manufacture of aliphatic anhydrides



Patented May 26, 1936 V I UNITED STATES PATENT OFFICE MANUFACTURE OF ALIPHATIC ANHYDRIDES Henry Dreyfus, London, England No Drawing. Application August 25, 1933, Serial No. 686,734. In Great Britain September 9, 1932 12 Claims. (01. 260123) This invention relates to the manufacture of composed in the presence of inert gases or vaaliphatic anhydrides, and especially to the manupors, as, for instance, nitrogen, or reducing gases facture of acetic anhydride, by the thermal deor vapors, such as carbon monoxide or hydrogen. composition of the corresponding acids. It will usually be found advisable to preheat I have found that the thermal decomposition the acid, whether in the liquid state under eleof aliphatic acids to produce aliphatic anhydrides vated pressure, or in the vapor phase, also under may be catalyzed by salts of oxy-acids of phospressure if desired, to a temperature approaching phorus, in which the phosphorus is present in or even approximately equal to the temperature a lower state of oxidation than .it is in phosphoric to be used for the decomposition. Such preheatlo acid. Preferably salts of phosphorous acid, such ing may be performed in any convenient way.

as calcium phosphite, magnesium phosphite, etc. Thus the acid vapors may be caused to pass are employed. If desired, however, salts such as through tubes or pipes heated to the required potassium hypophosphite, nickel pyrophosphite, temperature, or they may be passed through a chromic hypophosphite, or other salts of lower preheating bath, or any other method may be oxy-acids of phosphorus may be used. employed. 15 The decomposition of the acid according to The decomposition may be effected at any conthe invention may be effected in any convenient venient temperature. Usually temperatures beway. Thus for instance the acid vapor may be tween 400 C. and 900 C., and especially between caused to traverse tubes charged with the cata- 600 and 750 C., are very useful. Any suitable 2o lysts of the invention heated to the required temtype of apparatus may be employed, and such perature. The catalysts may if desired be emapparatus may be constructed of or lined with a ployed deposited on or otherwise in association metal such as copper, nickel, iron, or a nickel with inert carriers or filling materials, such as chromium steel, or with fireclay, fused silica, or kieselguhr, Carborundum, asbestos, silica gel, any other suitably resistant material.

pumice, etc., and they may also be employed to- After leaving the decomposition zone, the 25 gether with other substances favoring the dewater vapor and anhydride may be separated in composition, for instance calcium tungstate. any convenient way, preferably while the former In another method of applying the invention at least is still in the vapor phase. For instance, the acid vapors may be passed through a heated the anhydride may be separated by fractional bath comprising initially one or more of the catacondensation as described, for example, in U. S. 30 lysts of the invention. Such a bath may consist Patent No. 1,735,957, or the anhydride may be entirely or substantially entirely of the said catcondensed while the water vapor is removed by alyst or catalysts, or it may contain other submeans of the vapor of an entraining liquid, such stances which may or may not be catalysts for as benzene, carbon tetrachloride, petroleum the decomposition. Conveniently such a bath ether, etc. Again, the anhydride may be re- 35 may comprise metals such as lead or tellurium moved by means of a liquid in which it is soluble, or mixtures of metals together with one or more but water is insoluble, such as benzene, chlorooi the catalysts of the present invention, which form, etc. In a modification of this process, dismay be employed either in the molten or in the closed in U. S. Patent No. 1,915,573, the vapors solid state, according to the melting point of the from the reaction zone are caused to impinge on catalyst and the temperature employed for the the surface of a stream of such liquid. Another decomposition. method that may be employed, described in U. S. In yet another form of the invention the acid, Patent No. 1,817,614, consists in passing the recontaining the catalyst in suspension, may be inaction vapors over water binding substances jected or sprayed into the reaction zone. In such such as bisulphates, pyrosulphates, zinc chloride cases comparatively small amounts of the catalyst or calcium chloride or a phosphoric acid, prefare required; thus the acid may contain between erably at temperatures high enough to prevent 0.5% and 2% of the catalyst in suspension, alcondensation of the anhydride. Any other though other proportions may be employed. method of separation may, however, be em- In view especially of the readiness with which ployed. 50 the catalysts of the invention may, generally The invention is in no wise limited to the speaking, be oxidized, it is preferable to effect the manufacture of acetic anhydride, but may be decomposition of the acid in substantial absence applied to the manufacture of aliphatic anof oxidizing gases or vapors such as free oxygen hydrides in general. Thus, for instance, homoor air. If desired, however, the acid may be delogues of acetic acid, such as propionic acid, 55

butyric acid, etc., or substituted acetic acids such as methoxy acetic acid may be converted into their anhydrides by the process of the invention.

The following example illustrates the invention which is in no way limited thereby.

Example aliphatic anhydrides by thermal decomposition of the corresponding lower aliphatic carboxylic acids, the step of catalyzing the decomposition by a salt of an oxy-acid of phosphorus, in which the phosphorus is present in a lower state of oxidation than it is in phosphoric acid, which salt is stable at the decomposition temperature;

2. Process for the manufacture of lower fatty anhydrides which comprises subjecting the corresponding acids to thermal decomposition in the presence of a salt of an oxy-acid of phosphorus in which the phosphorus is present in a lower state of oxidation than it is in phosphoric acid, which salt is stable at the decomposition temperature.

3. Process for the manufacture of acetic anhydride which comprises subjecting acetic acid to thermal decomposition in the presence of a salt of an oxy-acid of phosphorus in. which the phosphorus is present in a lower state of oxidation than it is in phosphoric acid, which salt is stable at the decomposition temperature.

4. Process for the manufacture of lower aliphatic anhydrides which comprises subjecting the corresponding lower carboxylic acids to thermal decomposition in the presence of a salt of phosphorous acid, which is stable at the decomposition temperature.

5. Process for the manufacture of lower fatty anhydrides which comprises subjecting the corresponding acids to thermal decomposition in the presence of a salt of phosphorous acid which is stable at the decomposition temperature.

6. Process forthe manufacture of acetic anhydride which comprises subjecting acetic acid to thermal decomposition in the presence of a salt of phosphorous acid which is stable at the decomposition temperature.

7. Process for the manufacture of lower fatty anhydrides, which comprises subjecting the corresponding acids to thermal decomposition at a temperature between 600 and 900 C. in the presence of an alkali metal salt of phosphorous acid.

8. Process for the manufacture of acetic anhydride, which comprises subjecting acetic acid tothermal decomposition at a temperature between 600 and 900 C. in the presence of an alkali metal salt of phosphorous acid.

9. Process for the manufacture of acetic anhydride, which comprises subjecting acetic acid to thermal decomposition at a temperature between 600 and. 750 C. in the presence of an alkali metal. salt of phosphorous acid.

10. Process for the manufacture of lower fatty anhydrides, which comprises subjecting the corresponding acids tothermal decomposition at a temperature between 600 and 900 C. in the presence of an alkaline earth metal salt of phosphorous acid.

11. Process for the manufacture of acetic anhydrid'e, which comprises subjecting acetic acid to thermal decomposition at a temperature between 600" and 900 C. in the presence of an alkaline: earth metal salt of phosphorous acid.

1'2.v Process for the manufacture of acetic anhydride, which comprises subjecting acetic acid to thermal. decomposition at a temperature betWeen 600- and 750 C. in the presence of an alkaline earth metal salt of phosphorous acid.

HENRY DREYFUS. 

